The present invention relates to a detection device for use in an image forming apparatus such as a facsimile machine, and more particularly, to the detection device in which a light reflection type sensor is mounted on a control board, and capable of detecting transportation of a sheet medium or capable of detecting moving or operating phase of various movable segments used in the image forming apparatus.
In an image forming apparatus, various detection devices are provided. One of the detection devices detects existence of a sheet medium such as an original sheet which carries an original image and a printing sheet on which the original image is to be copied. Another detection device is adapted to detect passage of the sheet medium, and still another detection device is adapted to detect operating phase of a movable member such as an arm, a cover, etc. As such detection devices, available are a microswitch, a proximity switch which detects a moving phase of an actuator, photo-switch having a photo-interrupter, and a reflection type sensor.
The reflection type sensor includes a light emitting portion and a light receiving portion. Further, an actuator having a reflection plate is provided. The actuator is movable toward and away from the reflection type sensor in response to the passage of the sheet medium or in response to the movement of a movable member in the image forming apparatus.
If the sheet medium or the movable member reaches a predetermined area, an actuator reaches a predetermined region in the vicinity of the reflection type sensor so that the light from the light emitting portion can be impinged on the reflection plate and reflected toward the light receiving portion in order to detect the movable member or the sheet medium. Further, a board exclusively connected to the reflection type sensor is connected to a control board via a harness for processing signals from the reflection type sensor.
However, in the conventional detection device using the reflection type sensor, the actuator may provide relatively large moving stroke, and is required accurate positioning between the reflection type sensor and the actuator, when the latter is moved to a close position of the sensor, otherwise erroneous detection results. In order to avoid this drawback, high dimensional accuracy and accurate assembly work are required, which however, raises production cost of an entire image forming apparatus.
The photointerrupter can be used as the detection device instead of the reflection type sensor. However the photointerrupter is rather expensive and it would be rather difficult to form a slit.
In another aspect, a conventional facsimile machine includes a main frame having an upper open end and a cover member adapted to open or close the upper open end. The cover member includes a recording sheet cover for opening and closing an upper open end of a recording sheet accommodating portion and a panel cover for covering an operation panel. A detection device is provided for detecting open state of the recording sheet cover so as to prevent the facsimile machine from being operated with the recording sheet cover being open. Further a second detection device is provided for detecting open state of the panel cover to prevent the facsimile machine from being operated with the panel cover being open.
The second detection device in addition to the first detection device increases mechanical parts and production cost. However, the second detection device is an essential mechanism for checking white color level in an original reading process. More specifically, in the facsimile machine, white color level check data are used for checking white color level to determine threshold level so as to binarize image data obtained through reading an original image. The white color level check data are not permanently stored in an EEPOM but is stored in an economical RAM, so that white color level checking can be performed each time the original image is read. In the latter case, the panel cover must be closed during the white color level checking, otherwise the ambient light may be trapped in the checking. Still however, the mechanism for detecting opening phase of the panel cover should be dispensed with in terms of production cost.